The present invention relates to a television signal scrambling apparatus which scrambles a television signal in a so that it may be securely transmitted.
Conventionally, many different methods have been proposed for a scrambling a television signal. One of these is the line rotation method. In this method, as disclosed in U.S. Pat. No. 4,070,693, a horizontal video portion not including the horizontal sync signal and the burst signal is segmented into two parts which are exchanged with each other before their transmission. The segmentation of the horizontal video portion into two parts is accomplished at random for each scanning line.
However, this method has the following disadvantages. First, since a segmented point in the television signal is limited to the video portion, the horizontal sync signal appears at the regular interval even after scrambling and, thus, synchronization can be easily accomplished by an ordinary receiver. As a result, the scrambling effect is not necessarily sufficient. Next, in a scrambled video waveform, a waveform level at the segmented point is abruptly changed from a blanking level (pedestal level) and, thus, a transient error often occurs. As a result, after the demodulated is at the receiver, this an annoying glitch appears on the television screen.